1. FIELD OF THE INVENTION
This invention relates to a pig for cleaning a pipe or pipeline.
For the sake of simplicity, in the following, the term "pipeline" is used to describe a conventional pipeline or pipes used to convey fluids, e.g. in industrial heaters or cooling systems.
2. DISCUSSIONS OF THE PRIOR ART
Pipelines are commonly used to transport, inter alia, crude oil, gas, slurries or water. During use, the interior of a pipeline becomes coated which decreases flow through the pipeline. Typical coatings include paraffin, asphaltene, sediments, silica, coke, calcium or other salts and corrosion products which are often difficult or almost impossible to remove. The standard method of cleaning a pipeline is to drive a so-called pig through the pipeline using fluid pressure as the driving force. Pigs can also be used as dividers when transporting different materials through the pipeline, the pig simultaneously cleaning the interior of the pipeline.
Examples of pipeline cleaning pigs are described in U.S. Pat. Nos. 2,447,966, issued to D. K. Stephens on Aug. 24, 1948; 3,204,274, issued to M. M. Knapp on Sep. 7, 1965; 3,277,508, issued to M. M. Knapp et al on Oct. 1, 1968; 3,389,417, issued to M. M. Knapp et al on Jun. 25, 1968; 3,538,531, issued to M. M. Knapp et al on Nov. 10, 1970; 3,605,159, issued to H. J. Girard on Sep. 20, 1971; 3,659,305, issued to M. D. Powers on May 2, 1972; 3,725,968, issued to M. M. Knapp et al on Apr. 10, 1973; 3,863,287, issued to K. M. Knapp et al on Feb. 4, 1975; 4,077,079, issued to M. M. Knapp on Mar. 7, 1978; 4,244,073, issued to S. Sagawa on Jan. 13, 1981; 4,509,222, issued to K. M. Knapp on Apr. 9, 1985 and 4,603,449, issued to K. M. Knapp on Aug. 5, 1986.
In general, many existing pipeline pigs are incapable of cleaning deposits much harder than candle wax. Those pigs which are adapted to clean hard deposits such as sediment and scale are not able to maintain a seal between separate products in a pipeline, and are prone to tearing on welds or other irregularities on the interior of the pipeline.